The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Vehicles include an internal combustion engine that generates drive torque. More specifically, the engine draws in air and mixes the air with fuel to form a combustion mixture. The combustion mixture is compressed and ignited to drive pistons that are disposed within the cylinders. The pistons rotatably drive a crankshaft that transfers drive torque to a transmission and wheels. A knock sensor generates a knock signal based on a vibration of the engine. Disturbances in the knock signal, such as from background noise, can cause inaccurate engine knock determinations and, therefore, may cause one or more vehicle subsystems to operate inefficiently.
Conventional methods of processing the knock signal for background noise include moving averages methods, first order lag filters, and a full standard deviation computation. The use of a full standard deviation computation method provides superior description of the sample distribution to the moving averages methods and the first order lag filters. A commonly known equation for the full standard deviation includes:
                              Standard          ⁢                                          ⁢          Deviavtion                =                                            [                                                                    ∑                                          i                      =                      1                                                              i                      =                      N                                                        ⁢                                                            (                                                                        d                          i                                                -                                                  d                          _                                                                    )                                        2                                                                    (                                      N                    -                    1                                    )                                            ]                                .                                    (        1        )            Where di is a sample point, d is the average of the sample points, and N represents the number of sample points. This full standard deviation computation method requires a buffering for every point that is part of the distribution or alternatively using highly throughput-intensive data manipulation in order to produce an average and standard deviation. Thus, to achieve superior signal processing, large amounts of controller memory and throughput must be added. Increased processor throughput and additional memory can be costly to the controller.